#include <stdio.h>
int main(){
	double a=1.0,b=2.0;
	double sum=0.0;
	for(int i=1;i<=20;i++){
		sum+=b/a;
		double temp=a+b;
		a=b;
		b=temp;
	}
	printf("sum=%lf",sum);
	return 0;
}